1. Field of the Invention
The present invention relates to a photo-sensitive etchant and a method for forming metal image using the same.
The term "metal images" as used herein in the present specification means metal images in which image areas or non-image areas form depressions or projections and can be visually distinguished from each other, or means images comprising at least in part metal in which image areas or non-image areas can be visually or physically distinguished from each other by the difference in the material, and/or the physical property.
2. Description of the Prior Art
Metal images have so far been utilized in various fields. In general, metal images are formed by a photoetching method. For example, they are formed by providing a film of a light-sensitive substance such as a photosensitive polymer on a plate or film of a metal such as aluminum, subjecting the plate or film of the metal having the light-sensitive substance thereon to image-exposure to harden the exposed areas of the light-sensitive film, washing away the non-hardened unexposed areas with an organic solvent, etching (or engraving) the uncovered areas (where the metal surface is exposed) with an etchant or bringing the areas into contact with a solution containing an ingredient capable of reacting with the metal to thereby change the surface properties (i.e., to convert the metal in the surface portion to another substance by reaction with this ingredient), and then removing the hardened film covering the light exposed areas.
However, in the above-described method for forming metal images by a photoetching method, even the hardened film is also weakened in practice upon removing the film in the non-hardened areas to such an extent that in some cases the hardened film is also removed. Therefore, where extremely fine hardened areas exist, i.e., in order to obtain metal images having fine areas, extremely skilled techniques are required.
Heretofore, as an improved photoetching method, photosensitive etching solutions and methods which enable both exposure and etching to be conducted at the same time, as disclosed in U.S. Pat. Nos. 3,095,332, 3,346,384, 3,482,975, 3,482,976, 3,494,768, etc., have been suggested. However, in these methods, since a liquid or gaseous photo-sensitive etchant is continuously supplied between a photomask and a metal film, it is difficult to conduct the reaction of the fluid state light-decomposition product with the metal film uniformly all over the film in a short period of time. In addition, it is impossible to enhance the accuracy of the images. Furthermore, in the case of forming a liquid photosensitive etchant layer, the surface tension between this layer and the metal film, the adhesion property and the like must be taken into consideration. Thus, the method, such as the method for coating the liquid photo-sensitive etchant, the coating apparatus, the exposing method, the exposing apparatus, etc. are complicated. In addition, a defect in that the liquid layer disturbs the light path results.
On the other hand, the etching of a metal film using a solid photo-sensitive etching layer comprising iodoform, polystyrene and benzene has also been suggested. However, in fact, the rate of this etching reaction is so slow that some metals are barely changed.
As a result of extensive investigations to remove the above-described defects with the conventional metal image-forming methods, the inventors have achieved the present invention.
That is, a primary object of the present invention is to provide a light-sensitive etching agent which can etch metal accurately and rapidly.
A second object of this invention is to provide a method of forming an image by using the light-sensitive etching agent of this invention.